BREAKING: Completely refactor Tower, borrowing heavily from clj18n (thanks asmala!)

See CHANGELOG for details.
Migrate all tests to new API, Expectations
Add (deprecated) v1 API to help ease migration
Bump version (2.0.0-alpha6)
Update README, CHANGELOG
Add date, time, dt parsing
Refactor `localize` style parsing
Bump version (2.0.0-alpha7)